[The glomerular endothelium and the development of diabetic glomerulosclerosis]

Cyclic AMP inhibits stretch-induced overexpression of fibronectin in glomerular mesangial cells

Glomerular hypertension is proposed to play an important role in the progression of various glomerular diseases. Glomerular mesangial cells are considered to be exposed to the stretch stress due to glomerular hypertension and are found to produce the excess amount of extracellular matrix (ECM) proteins including fibronectin when exposed to the mechanical stretch. Herein, we provide the evidence that cAMP-generating agents inhibit the stretch-induced overexpression of fibronectin through the inhibition of the stretch-induced activation of mitogen-activated protein kinases (MAPKs) in protein kinase-A-dependent manner. We also found that the mechanical stretch enhanced the binding of nuclear extracts to activator protein-1 (AP-1)-like sequences in the promoter region of rat fibronectin gene and this enhancement was also prevented by the cAMP-generating agent. These results indicate that the agents, which activate cAMP/protein kinase-A axis, may work protectively against the injury from glomerular hypertension in mesangial cells.

Glomerular alterations in experimental diabetes of the rat

To detect structural glomerular alterations in the early stages of diabetes mellitus glomeruli from young streptozotocin diabetic rats were studied by light microscopy with morphometric methods 2, 8, 12 and 24 weeks after induction of diabetes. It was found that there is a marked increase in the percentage mesangial surface as compared with the control animals already two weeks after induction of diabetes. The relative mesangial surface fraction was greater in the diabetic animals than in the controls at all test times. It was also demonstrated that the endothelial cell count was reduced in the diabetic animals in the first few weeks of the study. High-grade glycosuria and proteinuria were likewise observed in the diabetic animals. Hence the mesangium appears to be one of the glomerular structures which shows the first changes in the initial stages of diabetes mellitus. Possibly the most likely cause of the changes based on the present study is the diabetic metabolic state (or the insulin deficiency).